1. Field of the Invention
This invention relates to blend compositions of a neutralized sulfonated elastomeric polymer, a hydroxyalkyl carboxylate ester and a thermoplastic resin wherein the resultant composition has both improved physical and rheological properties such as compression set for blends exhibiting elastomeric characteristics and impact strength for blends exhibiting thermoplastic characteristics.
2. Description of the Prior Art
The blend compositions of the present instant invention relate to compositions having improved physical and rheological properties for fabrication on conventional type fabricating equipment.
The hydroxyalkyl esters of this invention may be schematically represented as follows: ##STR1## wherein C is one or more carbon atoms in one or more molecules comprising a polymer and is in the polymer backbone chain of carbon atoms or is in an acyclic, alicyclic, or aromatic group which is pendant to the backbone chain; R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, C.sub.1 to C.sub.18 straight and branched chain acyclic, alicyclic, aryl, alkylaryl, arylalkyl groups and functional derivatives thereof.
Products which have a limited concentration of ionic groups covalently bonded to one or more carbon atoms of one or more molecules comprising a polymer, when partially or completely neutralized with mono or polyvalent cations such as sodium, zinc, magnesium, lead, ammonium and quaternary ammonium compounds are generally referred to as ionomers. The ionic groups can be covalently bonded to carbon atoms comprising the backbone chain of the polymer, which chain of carbon atoms may be interrupted by hetero atoms such as oxygen, nitrogen and sulfur, or the ionic groups can be bonded to acyclic, alicyclic, or aromatic groups which are pendant to the backbone chain. Solid, gel-free ionomers differ from covalently crosslinked elastomers, such as vulcanized rubber, in that while ionomers can be elastomeric at ordinary temperatures, at elevated temperature they can be extruded, compression molded, blow molded, sheeted, vacuum formed and injection molded.
Sulfonated polymers are known to be relatively unstable and are difficult to process in safety or without degradation in conventional plastic or rubber equipment at elevated temperatures. Except for this tendency to degrade it would be advantageous to process the free acid since the weak ionic associations result in a low polymer viscosity permitting easy mixing with neutralizing agents, extender oils, plasticizers, and other polymers. Such oil extended systems can then be reacted with the neutralizing agent which is an amine or metallic or quaternary base such as an oxide or hydroxide or salt of a weak acid such as an acetate or stearate to yield the ionomer.
On the other hand, if the sulfonated polymer is first neutralized with a counterion and the ionomeric product isolated it is found to possess an extraordinarily high viscosity even at elevated temperatures commonly used for processing thermoplastic polymers in conventional equipment and must be mixed with other materials by solution techniques.
A major object of the instant invention is to provide a selected class of ionomers which can be blended with a minor amount of a thermoplastic resin to provide elastomeric blend compositions having superior physical and rheological properties.
Another major object of the instant invention is to provide a selected class of ionomers which can be blended in a minor portion into a thermoplastic resin for modulation and improvement of the physical properties of the thermoplastic resin.
A more specific object of the present invention is to provide solid, gel-free blend compositions of a neutralized sulfonated polymer, a crystalline polyolefinic thermoplastic and a hydroxyalkyl carboxylate ester, wherein the composition has improved processability on conventional plastic fabricating equipment as well as improved physical properties such as compression set. These, and other objects of this invention will be further apparent in the detailed description of the invention which follows below.
The reaction of an oxirane (e.g. ethylene oxide) with a sulfonic acid to form a hydroxyethyl ester is old in the art. U.S. Pat. No. 2,208,581 discloses the preparation of surface active agents by the reaction of low molecular weight sulfonic acids with a compound containing an olefin oxide.
In a first copending application concerning preparation of ionomeric latex epoxides are used to quench the sulfonation reaction and allow the cement to be processable in a unique latex process. However, this copending application fails to teach a method for the isolation of a solid, gel-free, hydrolytically stable polymeric hydroxyalkyl sulfonate having desirable physical and rheological properties, wherein these polymeric sulfonates are readily convertible to metal sulfonate during and after processing thereby permitting fabrication on conventional type equipment to a variety of useful articles. Furthermore, it is completely unpredictable that a solid, gel-free hydrolytically stable polymeric hydroxyalkyl sulfonate is capable of being isolated in a steam stripping operation under acidic conditions and at higher temperatures based upon the published literature on the hydrolytic stability of low molecular weight alkyl sulfonates. No references have been found in the chemical or patent literature for the preparation of hydroxyalkyl esters of polymeric sulfonic acids or for the preparation of ionomers from these esters by reaction with a basic compound or salt of an acid having a lower K.sub.a than the sulfonic acid.
In another copending application entitled "Polymeric Hydroxyalkyl Sulfonates" (U.S. Ser. No. 855,763 filed Jan. 29, 1977), the preparation of polymeric hydroxyalkyl sulfonates are described wherein an acid form of a sulfonated polymer is reacted with an oxirane having the general formula: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen and C.sub.1 to C.sub.18 straight and branched chain acyclic, alicyclic, aryl, alkylaryl, arylalkyl radicals and functional derivatives thereof. The improved blend compositions of the present instant invention provide materials of superior physical and rheological properties.
U.S. Pat. No. 3,974,240 and 3,974,241 teach the blend compositions of a crystalline polyolefinic thermoplastic and a neutralized sulfonated elastomeric polymer. These applications differ from the present application both in their method of manufacturing and their resultant composition. The use of the hydroxyalkyl carboxylate ester as a plasticizer in the blend composition results in definite improvements in processability on conventional type plastic fabricating equipment. In the present invention the polyolefinic thermoplastic is blended with the sulfonated polymer prior to neutralization wherein a molecular entanglement of the polymeric chains of the sulfonated polymer and the polyolefinic polymer is achieved thereby resulting in improved physical properties.